Riot since you are buffing Darius's ult, this idea the community agrees is the best buff for him

His ult would fully refresh on kill BUT it CANNOT be used on the person he killed for 120/100/80 seconds, cdr will reduce this.

So you dunk your laner, go home, come back to lane in the span 60 seconds, you have your ult up again but you CANNOT dunk them until another 60 seconds.

Say the enemy jungler ganks, you can dunk him but can't dunk your laner as the time is not up yet.

This is the idea that has been passed around for 2 years now as a buff to Darius and is the buff he should get until his rework is ready Riot, people agree this solves the low elo QQ and the unfairness of Darius dunking his lane opponent without end.

Since Meddler said they will lower the mana costs later, it could be something like for each consecutive ult, Darius needs 20 less mana for each dunk, going to 20 mana before the penta dunk.